Sudden cardiac death (SCD) is a major public health problem, accounting for at least 300,000 deaths yearly, and is the most devastating manifestation of heart failure (HF). Moreover, why some HF are prone to SCD and others are not is poorly understood. Accumulating evidence suggests that subtle beat to beat alternation of cardiac repolarization, evidenced clinically by T-wave alternans (T-ALT), is an important marker of susceptibility to SCD in HF. Interestingly, in the absence of alternans, patients with HF exhibit resistance to SCD. Therefore, the overriding aim of this proposal is to investigate molecular mechanisms for the development of cardiac alternans and potential novel therapies directed to target these mechanisms. Specifically, the applicant will utilized target gene therapy techniques to investigate the role of SERCA2a in the development of cellular alternans in normal and failing hearts. The following aims will be addressed: 1) Demonstrate a mechanistic relationship between SR calcium reuptake and cellular alternans. Specifically, the applicant will use viral-based in vivo gene transfer in the normal heart to enhance or impair calcium reuptake by increasing expression or silencing of SERCA2a. It is hypothesized that overexpression of SERCA2a in the normal heart will suppress calcium transient alternans (Ca-ALT) and Vm-ALT. Furthermore, silencing of SERCA2a will enhance Ca-ALT and Vm-ALT. 2) Characterize the relationship between impaired calcium cycling proteins and susceptibility to cellular alternans in the guinea pig pressure-overload model of HF. It is predicted that HF will enhance susceptibility to cellular alternans. 3) Use targeted gene therapy in the failing heart to restore cellular Ca cycling by manipulating expression of SERCA2a. This strategy will be employed to retard or eradicate the development of cellular alternans in the intact failing heart. Since cellular alternans is a consistent precursor to ventricular fibrillation (VF), the applicant's goal is to establish the proof of concept that the intact heart can be engineered which is resistant to VF. Such findings would introduce an entirely novel paradigm for arrhythmia therapy based on amelioration of cellular alternans. Moreover, this will be one of the first investigations of cardiac alternans in HF, the most common setting for SCD. [unreadable] [unreadable] [unreadable] [unreadable]